1. Field Of The Invention
The present invention relates to rotary shredders in general and more particular to high volume shredders used to shred waste material and being of a type having high torque, slow speed, and capable of producing small particle size materials in a single pass.
2. General Background
Typically, modular or slow speed shear shredders utilize a series of intermeshing cutting faces which shear material as it is captured by the cutters and pulled through the machine. Examples of such machines are taught by U.S. Pat. Nos. 5,402,950, 3,931,935, 5,145,120, 4,119,277, 4,690,337, 4,925,116, 5,062,576, 5,094,392, 5,248,100, and 5,402,948. Cutters, generally are of two types (1) teeth attached and arrayed around a rotatable cylindrical core or (2) comprised of heavy steel plates stacked on a mandrel. In either case the teeth shear material by shearing such material between an anvil and the tooth or between counter-rotating, intermeshing disk. It is this arrangement of teeth and the associated anvil and/or the configuration of intermeshing disk which determines the efficiency and particle size of the materials passing through the machines. During operation, the cutter's teeth are subjected to abrasion and wear from their shearing of material. The shear's teeth or hooks as they are sometimes called tend to round off along the cutting edges due to abrasion and wear. When this happens, the gap between intermeshing disks and/or anvils begins to open wider until the hooks or teeth are no longer capable of grabbing the infeed material effectively. The cutters begin to rip and tear instead of shearing and it often becomes necessary to replace the entire set of cutters in order to restore the performance of the shear machine. Excessive wear and damage to the cutters is a constant problem. Therefore, various apparatus have been employed to help alleviate such problems as can be seen in the ,337 and ,100 patents which employ movable anvils, while other such as the U.S. Pat. Nos. 4,946,109, 5,507,441, or ,277, ,950, and ,948 patents utilize replaceable cutter face blade or element. The ,948 patent provides a cutter bar having a plurality of carbide cutter elements along its length. In such cases where insertable cutting teeth are used, the arrangement and configuration of the teeth are restricted to a particular type and size due to their contact with a fixed anvil. In cases where replaceable inserts are used they are generally restricted to the face or edges of the cutter and are held in position with bolts or brazed to the cutter tooth. Such arrangements bring the bolt heads in direct contact with the material being sheared, resulting in lost inserts and/or making it difficult to remove the bolts for replacement.
Disk type, slow speed, shredders often require spacer disk between the cutter disk and a series of cleaning fingers to dislodge material build-up between the cutter disk. Other problems associated with this type shredder include shaft fracture due to large objects being pulled between a pair of counter rotating disk. To overcome such problems hydraulic drives and load sensors have been developed such as that disclosed in the ,100, and ,948 patents. However, in such cases the systems fail to address the need.
As mentioned above, In most cases slow speed, shredders pull material into the machine with the shredder teeth or the material is feed by a rotary feeder units such as that taught by the ,948 patent or to conveying systems line that disclose by the ,277 patent. However, such feeders are usually limited to small particles or simply serve to feed the material to the cutters. No attempt has been made to force feed materials to the cutters or to presize the material.
It is known within the shredder art that a center anvil, such as is taught by the ,392 patent, may be employed to assist in shredding which may also prevent material jams between the cutters and thus prevent rotating shaft fracture. However, the ,392 patent relies on a one piece unitized construction for its rotating cutters. There is also no provision made for replacement of the cutter teeth or wear surfaces of the cutter teeth or anvil.
Replacing cutters in shear shredders having cutters permanently attached to its rotating members requires complete disassembly of the shredder. Typically, replacement cutter assemblies plus the labor to install them is a very expensive procedure even for a small machine and much more costly for a large one. Therefore, one of the major drawbacks associated with shear shredder operation is the high cost of maintaining the equipment. Further, shear shredders tend to cut material into long strips. In cases where particle size is important, it becomes necessary to classify the shredded material and route all oversized material back through the shredder repeatedly until it is properly sized to exit the classification system. This repeated passing of material through a single shredder lowers the shredder's processing capacity and decreases the life of the cutters. The only alternative would be to simply stack shear shredders so that material can cascade through a number of shredders having increasingly narrower cutters. Usually, the capital cost of multiple shredders prohibits this approach. Therefore there is a need for a more efficient shredder system in which; the particle size can be controlled, the cutter teeth can be replaced readily, tooth configuration can be changed rapidly, and older machines can be rebuilt, incorporating new and improved efficient concepts at an economical cost.